Arc snuffing circuit



Oct. 14, 1941. H, cox ETAL ARC VSNUFFING cmcum Filed Aug. 2, 1940 WITNESSES:

INVENTORS' OJep/J Cox and Faber/1E?! myn e/l J JW ATTORNEY to eliminate the operation of Patented Oct. 14, 1941 UNITED STATES PATE Mr I OFFICE ARC SNUFFING CIRCUIT Joseph H. Cox and Robert R. Longwell, Forest Hills, P

a., asslgnors to Westinghouse Electric I: Manufacturing Company, a corporation of Pennsylv East Pittsburgh, Pa., ania Application August 2, 1940, Serial No. 349,658

verters difliculty has been experienced in securing arc snufilng with a reasonable bias potential, because it is necessary to connect the control potentials to each of the cathodes by means of a suitable balancing resistor and when one of the sections arcs back the potential of the faulty section falls substantially to zero but the potential of the cathode of the non-faulty section is maintained at a high potential by the positive bus. The positive potential of the non-faulty section maintains the connecting resistor at a high positive potential so that the application of a reasonable biasing potential is not sufficient the control grids either in grid controlled devices or in the firing tubes of make-alive devices.

Inthe construction according to our invention, this difficulty is eliminated by fault responsive switching connections which disconnect the non-faulty section from the equalizing resistor and connect all of the grid circuits directly to the cathode of the faulty section so that a reasonable biasing potential is sufficient to snuif the arc in the faulty section. Obviously the control potentials are even more negative with respect to the non-faulty section but it is usually desired to momentarily interrupt all sections, in order to clear the effects of the fault.

It is, accordingly, an object of our invention to provide a control system for applying negative potential to block the fault in a sectionalized converter.

It is a further object of our invention to provide a fault responsive switching system for so connecting the biasing potentials that a reasonable biasing potential will alleviate the fault conditions.

Other objects and advantages of our invention will be apparent from the following detailed description taken in conjunction with the accompanying drawing, in which the single figure is a schematic illustration of a vapor electric converter utilizing our invention.

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In the illustrative embodiment of our invention an alternating current circuit i is connected to a direct-current circuit 2 by means of a connecting transformer 3, which connecting transformer 3 has a plurality of substantially inde pendent secondary winding groups 4 and I. For simplicity of illustration we have shown the secondary winding groups 4 and 5 as being of identical construction. However, it is obvious that they may be of dissimilar construction in .order 5 of the connecting transformer l is connected to a valve type converter A or B, herein illustrated as of a make-alive type, each converter section A or B having a plurality of substantially identical make-alive type valves 8. Each of the make-alive type valves 6 comprises a main anode 1, a cathode 8 and a make-alive electrode 9 for determining the conductivity of the valve I.

A suitable source of control potential is pro vided for connection to the make-alive electrodes 9. For simplicity of illustratio we have shown so-called anode firing. That is, the make-alive potential is secured from the main anode circuit. However, it is obvious that any suitable source of control potential can be utilized and in normal construction the control potential is secured from a suitable control transformer (not shown).

The application of the control potential is determined by means of grid controlled firing tubes III in series between the control potential and the make-alive electrodes 9. Suitable firing transformers H and I2 are provided for supplying control potentials to the grids, ll of the dring tubes I 0. Obviously in the application of grid controlled rectifiers, these firing transiormers H and I! are directly connected to the control grids-of the main valves of the converter.

Each converter section A and B is connected to the direct-current bus 2 by means of suitable circuit breakers 12A and 12B responsive to inverse current through the breaker. In normal operation the firing transformers II and I! are 4 connected to the respective cathodes 8 of the converter sections A and B by means of a suitable balancing resistor H. The balancing resistor I4 equalizes the potential between the oathodes and supplies a return transformers II and I2;

Suitable current transformers it are associated with the alternating current leads of the connecting transformer 3 and a fault responsive relay 5| is energized by the potentials of the current transformers I5. In the event of fault.

circuit for the firing formers Ii and I2. rence of a fault in fault in any section in eitherof the converter sections A or B, the

fault responsive relay 5| picks up and applies a biasing potential'which may be secured from any suitable source herein illustrated as an auxiliary full wave rectifier able alternating current source hating-current circuit I.

Upon the closing of relay iii, the source i8 is connected across the resistor which applies the biasing potential between the balancing resister l4 and the midpoints of the firing trans- However, during the occurone of the converter sections, such as section A, the cathode potential of the faulty section A falls substantially to zero and the breaker 12A, associated withthat section opens but the bus ode of B at normal bus potential and the midpoint of the balancing resistor M will be at a positive potential with respect to the cathode of A by roughly one half of the bus potential, which is greater than can be overcome by a reasonable negative biasing potential from the direct current source l6 unless means are provided to disconnect the resistor of the non-faulting section. a l

To eliminate the positive bias during the faulty period, we have provided each of the breakers 12A and 123, with a plurality of contacts so arranged that when both 12A and 12B are open, the balancing resistor I4 is connected to the respective cathodes of A and B by means of the back contacts 12A]; and 1281 of the breakers 12A and 12B. Likewise when 12A and 12B are closed, the'balancing resistor ll connects the respective cathodes through the front contacts "Au and 12150. However, on the occurrence of a such as section A, 12A opens, opening its front contact "Au and closing its back contact 12A!) so that the balancing resistor i4 is: connected only to the cathode of the faulty section A and disconnected from the cathode of of'the non-faulty section B.- The full negative potential of the biasing source I6 is then applied between the cathode of the faulty section A and tizi'e midpoints of the firing transformers H and l Obviously, this potential is also applied to the midpoints of the firing transformer associated with section B as well as that of section A. However, since it is usually desirable to terminate current flow in both or all of the parallel sections, this application is desirable.

In the event it is desired to close or terminate the operation of any section while permitting the operation-of the remaining sections suitable disconnecting switches 89A and 89B are provided in series with the respective cathodes of sections A and B.

When the disconnecting switches 89A and 89B are closed, the potentials of the respective cathodes are applied to the balancing resistor H! by meansof the front contacts MM and 8913a carriedby the disconnecting switches 89A and 89B. However;-when one of the disconnecting switches such as 89A is open, the front contacts MM is such as the alterop ned and-the back contact 89Ab is closed to disconnect the balancing resistor I4 from the 'cathode'of the inactive section A and lock in the balancing resistor l4 to the cathode of the operation-section B.

+111 this manner our invention secures the application i= negative potential of a reasonable valuein c der tosecure blocking of the converter inrspo'nse to the current fault in either section,

i6 supplied from a suit- II from the cathode 8' parting from the true spirit of our invention or of vapor 2 tends to maintain the cath-,

the scope of the appended claims.

We claim as our invention:

1. An electric current conversion system comprising a plurality of parallel connected groups electric valves, a control electrode forv each of said valves, control-means for periodically and successively applying a potential of the proper polarity to said valves to successively render the valves of the several groups conducting, a balancing impedance for connecting said control means to the cathodes of the several groups of valves, a source of biasing potential,

fault responsive relay means for connecting the potential of said source between said balancing resistor and said control means, a fault responsive circuit interrupter in series with each group of valves and auxiliary contacts carried by each circuit interrupter for connecting the balancing impedance only to the faulting group in the event of fault actuation of the circuit interrupter.

2. An electric current conversion system comprising a plurality of parallel connected groups of vapor electric valves, a control electrode for each of said valves, control means for periodically and successively applying a potential of the proper polarity to said valves to successively render the valves of the several groups conducting, a balancing impedance for connecting said potential of said source between said balancing resistor and said control means, a fault responsive circuit interrupter in series with each group of valves and auxiliary contacts carried by each circuit interrupter for connecting the balancing impedance only to the faulting group in the event of fault actuation of the circuit interrupter, a sectionalizing switch in series with each group of valves and auxiliary contacts carried by the sectionalizing switch such that opening the sec- :ionalizing switch locks out the disconnected sec ion.

3. A vapor electric converter comprising a plurality of parallel operating sections, each section containing a plurality of similar electric valves, a control electrode for each of said valve control means for periodically impressing potentials on said control electrodes for determining the conductivity of said valves, a fault responsive circuit breaker in series with each section of said converter, a balancing resistor, auxiliary contacts carried by said circuit breakers for connecting said balancing resistors to the several cathtial effective to block operation of the valves of the converter. I

4. A vapor electric conversion system comprising' a plurality of parallel operating sections, each section including a plurality of electric valves, a firing transformer for controlling the conductivity of said valves, means including a balancing resistor for connecting said firing transformer to the cathode of said valves, a fault responsive circuit breaker in series with each section of said converter, switching means actuated by said fault responsive circuit breakers, said switching means being operative to disconnect the balancing resistor from the non-faulting sections in the event of fault in one of the sections, a source of biasing potential and a fault responsive relay for connecting said biasing potential to said firing transformer.

5. A vapor electric conversion system comprising a plurality of parallel operating sections, each section including a plurality of electric the balancing resistor to the disconnected secbalancing resistor for connecting said firing transformer to the cathode of said valves, a fault responsive circuit breaker in series with each section of said converter, switching means actu ated by said fault responsive circuit breakers, said switching means being operative to disconnect the balancing resistor from the non-faulting sections in the event of fault in one of the sections, a source of biasing potential and a fault responsive relay for connecting said biasing potential to said firing transformer, a disconnect switch in series with each section of the converter and auxiliary contacts carried therebyto render said fault responsive breakers ineifective to connect tion.

JOSEPH H. COX. ROBERT R. LONGWELL. 

